1. Field of the Invention
The present invention relates to an optical pickup apparatus used for recording and reproducing on an optical disc, an optical pickup apparatus using light sources having different wavelengths for the purpose of corresponding to recording mediums having different recording densities and an optical disc apparatus using the optical pickup apparatus.
2. Description of the Related Art
An optical recording medium has become rapidly popular because advantages that a recording capacity thereof is great and a treatment is easily executed are recognized. Further, in order to increase a recording capacity, various kinds of recording mediums have been proposed. On the other hands, a demand of a disc apparatus capable of corresponding to these kinds of recording mediums has been increased. In response to the demand mentioned above, an optical pickup disclosed in JP-A-10-154344 has been proposed as an optical structure using light sources having two kinds of different wavelengths.
Long and short of it is that two kinds of light sources having the different wavelengths are prepared, an objective lens corresponding to an optical performance of a high density recording medium is provided, and the same objective lens is commonly used for a low density recording medium by forward shifting a position of a light source having a long wavelength so as to set an incident light flux to the objective lens to a fine divergent light.
However, since a medium capable of recording as a low density recording medium is going to be supplied to a market, there is a limit for recording under an optimum condition only by a structure of commonly using the objective lens. In particular, since the incident light to the objective lens is the fine divergent light in the low density recording medium, a coma aberration caused by a displacement of an optical axis is increased at a time of shifting (particularly shifting a tracking of) the objective lens, so that a considerable influence is applied to recording a signal recorded on the medium (including both of the case of simply reproducing and the case of reproducing a control signal required for recording).
Accordingly, the present invention is made for the purpose of solving the problem mentioned above, and an object of the present invention is to provide an optical pickup apparatus which can reproduce a high-quality signal from a medium even in a state of maintaining a simple optical structure of the optical pickup disclosed in the technology mentioned above, and an optical disc apparatus using the optical pickup apparatus.
In accordance with the present invention, there is provided an optical pickup apparatus reproducing a recording information of an optical disc or recording the information comprising:
an optical unit having a light source radiating a laser beam and an optical detector detecting a reflected light from the optical disc;
a collimator lens converting the radiated light of the light source into a fine divergent pencil of rays; and
an objective lens,
wherein the collimator lens forms a wavefront shape forming a fine divergent light and a wavefront shape correcting a coma aberration, and the wavefront shape correcting the coma aberration is formed in a wavefront shape correcting more coma aberration in correspondence to an increase of radius of the collimator lens.
In accordance with the present invention, it is possible to restrict a generation of the coma aberration even when the objective lens is shifted, so that a jitter generated together with the lens shift is not increased, and a tracking error (TE) signal can be maintained with a high quality. As a result, an accuracy of recording position is improved, a loss of an optical power is restricted at a time of recording, and an excellent optical pickup apparatus can be obtained.